The overall objective of the program is a detailed study of congenital abnormalities of the visual pathways that occur in a number of different mammalian species including the human. Animals lacking pigment in the retinal pigment epithelium develop abnormal retinofugal pathways. The development of the earliest retinofugal axons is being studied between the eye cup and the optic chiasm, and special attention is being paid to situations in which the axons may relate to pigmented cells. The structure of the optic chiasm is being studied in abnormal cats and mice, and also in birds having an appropriate pigment deficit. The distribution of the retinogeniculate pathway is being studied in Siamese cats and in mink, and the geniculocortical pathways, which also show abnormalities related to the abnormal retinofugal pathways, are being studied in mink. In addition, the development of corticogeniculate pathways is being studied in abnormal cats using fiber degeneration and autoradiographic methods.